As of June 1, 2009, via brainstorms with associates and testing on my own, I believe that these are currently the top 10 reasons why a Website ranks well at Google:
1. In-bound Links from Diverse Topically Related Domains
2. Keyword Usage with Prominence in Page Title
3. In-bound Link Anchor Text (Reputation)
4. Social Media / Blog Presence
5. In-bound Links from Topical Authorities (Your Industries: Directories, Forums, and High PR Pages)
6. Content Optimization and Theming
7. Age and History of Domain and Traffic Data
8. Growth and Freshness
9. Clean Code
10. Vertical Search Presence (News, Groups, Video, Local/Mobile, etc.)